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We have to climb a mountain in order to conquer it. In quantum physics there is a different way: objects can reach the opposite side of a hill simply by tunnelling through it, instead of laboriously climbing over it. An international team of researchers working with Prof. Ferenc Krausz from the Max Planck Institute for Quantum Optics has now observed electrons in this tunnelling process. This effect is responsible for the ionization of atoms under the influence of strong magnetic fields. The electrons overcome the attraction of the atomic nucleus by tunnelling through a potential wall. The scientists used ultra-short laser pulses to show discrete stages of ionization in this process, each of which lasts 100 attoseconds - a fraction of a billionth of a second. The results make a significant contribution to understanding how electrons move around in atoms and molecules.

In the same way as gravity brings a body to a halt on the floor of a valley, the nuclear force (which binds protons and neutrons to form the atomic nucleus) and the electrical force (which combines negatively charged electrons with the positively charged atomic nucleus to make an atom) hold these particles within a tiny space. This binding effect can also be depicted as a type of valley, which is also called a potential by physicists. In the world of quantum particles, it is, to a certain extent, a normal event to tunnel through the wall surrounding the potential well. An international team of researchers working with Ferenc Krausz has now caught the electrons in the act of tunnelling through the binding potential of the atom nucleus under the influence of laser light. The physicists used the new tools provided by attosecond metrology. "For the first time, our findings confirmed in real time observation the theoretical predictions of quantum mechanics," says Ferenc Krausz, Director at the Max Planck Institute for Quantum Optics and head of the team of scientists.

Figure 2: The electrical field of a laser pulse exerts a strong force on an electron located at the edge of an atom (green cloud around the nucleus).This force changes...Click here for more information.

The tunnelling effect can be explained by the wave behaviour of each particle. Macroscopic objects are extremely unlikely to tunnel, which is why the phenomenon has never been observed in them. In contrast, there is a significant probability that particles from the microcosmos will tunnel through areas where, according to the rules of traditional physics, they are not even supposed to be. The tunnelling effect is considered to be responsible for processes as varied as atomic nuclei decay and the switching process in electronic components. However, since it only lasts for an extremely short time, it has not yet been observed in real time.

Krausz and his colleagues have now followed this process live with the aid of two light pulses: an intense pulse of just a few wave trains of red laser light and an attosecond pulse of extreme ultraviolet light perfectly synchronized with the red pulse. The electrical field of the laser pulses periodically exerts strong forces on the electrons. When the force is at its strongest, the light force presses the potential wall downwards. For a short moment when the wave peaks, the electron has the opportunity to penetrate the barrier and escape from the atom. This opportunity only arises when the wave peaks, that is over an extremely short interval of a fraction of a femtosecond, a trillionth of a second.

Figure 3: Each time a wave peak hits the atom, the probability that an electron will be progressively released within a few 100 attoseconds increases. This phenomenon, which was predicted...Click here for more information.

There is no instrument that can directly resolve the tunnel effect. It is only possible to show the existence of the end products, the atoms, which, following the laser pulse, disintegrate into an electron and a positively charged ion. The researchers therefore had to use the trick of experimenting with neon atoms. In these, the electrons are in a closed shell, and therefore in particularly strong bonds, and resist the attempts of the laser pulse to release them from the atom. Only electrons hit by an attosecond flash of UV manage to reach the periphery of the atom and can extricate themselves from the atom by tunnelling. Therefore, the physicists can only ionize neon atoms with a red laser pulse that they have first prepared with this flash.

"With a UV pulse lasting just 250 attoseconds, which was synchronized exactly with the red laser pulse, we moved an electron at any point in time during the laser wave with attosecond precision to the periphery," explains Krausz. Step by step, the researchers shifted this point in time and measured the number of atoms ionized by the laser. This allowed them to reconstruct the chronology of the ionization process. As the theory predicted, the electrons left the atoms in the immediate vicinity of the most intense wave peaks, which can be seen clearly from the discrete stages of ionization coinciding exactly with the peaks in fig. 3 (the green line). The electrons remained at this stage for less than 400 attoseconds. Within such a short period, the electrons are released from the atom by the light energy.

"The experiments not only provide us with insight into the dynamics of electron tunnelling for the first time," says Krausz. "We have also shown that the movement of electrons in atoms or molecules can be observed in real time with the aid of laser field-induced tunnelling." Based on this finding and the enabled control over electron movement within the atom, in the future scientists will be able to research how the boundaries of microelectronics can be shifted, or how to develop sources of compact, very bright X-rays. These will in turn allow progress to be made in the imaging of biological objects and in radiation therapy.

"Physical reality” isn’t some arbitrary demarcation. It is defined in terms of what we can systematically investigate, directly or not, by means of our senses. It is preposterous to assert that the process of systematic scientific reasoning arbitrarily excludes “non-physical explanations” because the very notion of “non-physical explanation” is contradictory.

Sometimes I wonder whether it was a good idea to drop studying string theory and subatomic particles and study cells and enzymes instead. But I still retain a keen interest in the bizarre world of the quantum. Call it a sort of side-science for me, half reality, half theoretical. The fact that we can observe quantum tunnelling is testimony to how far ahead the Europeans are, with CERN and all that. What I'm really waiting for are three big discoveries that could be the discoveries of the century namely,

M/String theory

detection of Dark Energy: this is currently being done in 10 underground labs across the world, where scientists have set up these ultra-fine metallic germanium structures cooled to 1/70,000th of one Celcius degree above absolute Zero, and waiting for a Dark Matter particle (that's a WIMP or Weakly Interacting Massive Particle) to strike it and cause a detectable heat spike. So far, nothing yet.

and lastly

Confirmation of the Multiverse interpretation. This would coincide with the M theory GUT (General Unifying Theory), because if the 11-dimensional hyperspace String theory is correct, then the Multiverse must also be correct. Which would be cool because there are no laws of physics stopping us from travelling to another universe, which is good because ours wil eventually die.

So yeah, it's cool.

"Physical reality” isn’t some arbitrary demarcation. It is defined in terms of what we can systematically investigate, directly or not, by means of our senses. It is preposterous to assert that the process of systematic scientific reasoning arbitrarily excludes “non-physical explanations” because the very notion of “non-physical explanation” is contradictory.

Only one problem with string theory, more physicists seem to be turning a skeptical eye to this field. They have been 5yrs out from a laboratory testable experiment for the last twenty years. I would love to seem something of substance come from this field of study, and maybe it will with CERN. There was a book written last year regarding the lack of anything testable in string theory called "Not Even Wrong". I haven't read it but would like to when I get caught up with my reading.

I chose String theory because it is the only serious candidate at the moment for a TOE (theory of everything), a goal towards which physics is constantly striving.

"Physical reality” isn’t some arbitrary demarcation. It is defined in terms of what we can systematically investigate, directly or not, by means of our senses. It is preposterous to assert that the process of systematic scientific reasoning arbitrarily excludes “non-physical explanations” because the very notion of “non-physical explanation” is contradictory.

I chose String theory because it is the only serious candidate at the moment for a TOE (theory of everything), a goal towards which physics is constantly striving.

Oh don't get me wrong, the theory is fascinating. It appears to have great potential and the math seems to be there. I was just stating, from what I have heard in the last year or so, there seems to be a building skepticism of whether string theorists will be able to produce a testable hypothesis.

I still think this avenue should be pursued. This is what I love about science, it's ability to question from within while remaining open to new information. Unlike dogmatic religions.

Well, I have now read this article three times. I am fairly certain it is written in English, but that is about all I can discern. Perhaps if I print it and put it under my pillow, the physics fairy will sprinkle some dust on my head so I understand it.

BGH, it really does sound fascinating and exciting and I only have one question: does this get me any closer to "beaming up"? lol

Perhaps you could suggest some beginner physics books/references for me? Thanks!

Thanks!! I will be reading an essay that RigorOMortis recommended this weekend. If my science teachers in high school had been this interested and patient with me I would have studies science more closely. I will catch up with you all eventually!

What I'm really waiting for are three big discoveries that could be the discoveries of the century namely,

M/String theory

detection of Dark Energy: this is currently being done in 10 underground labs across the world, where scientists have set up these ultra-fine metallic germanium structures cooled to 1/70,000th of one Celcius degree above absolute Zero, and waiting for a Dark Matter particle (that's a WIMP or Weakly Interacting Massive Particle) to strike it and cause a detectable heat spike. So far, nothing yet.

Just wanted to comment on the Dark Energy. In modern (really modern, I'm talking about the discoveries and advances of the last 5-10 years) cosmology it's very evident that Dark Energy exists and that this Dark Energy causes our universe to expand (though the energy per m³ is very small, imagine this small value throughout the hugeness of the entire universe). We can confidently state this on a scientific basis, even without "proving" it's existance directly in experiments. There are a number of observations that leads to this conclusion. If you're interested I can write more about this later (given I have time + it's 5am gotta sleep ffsl ;P). Anyway, science rocks!

Just wanted to comment on the Dark Energy. In modern (really modern, I'm talking about the discoveries and advances of the last 5-10 years) cosmology it's very evident that Dark Energy exists and that this Dark Energy causes our universe to expand (though the energy per m³ is very small, imagine this small value throughout the hugeness of the entire universe). We can confidently state this on a scientific basis, even without "proving" it's existance directly in experiments. There are a number of observations that leads to this conclusion. If you're interested I can write more about this later (given I have time + it's 5am gotta sleep ffsl ;P). Anyway, science rocks!

They have found new very good, visual evidence for dark energy using hubble imaging.

Researchers find evidence of dark energy in our galactic neighborhood

Astrophysicists in recent years have found evidence for a force they call dark energy in observations from the farthest reaches of the universe, billions of light years away. Now an international team of researchers has used data from powerful computer models, supported by observations from the Hubble Space Telescope, to find evidence of dark energy right in our own cosmic neighborhood.

Image: A supercomputer-produced cross-section of part of the universe shows galaxies as brighter dots along filaments of matter, with a sea of dark energy filling in between the galactic islands. (Credit James Wadsley, McMaster University, Hamilton, Ontario)

The data paint a picture of the universe as a virtual sea of dark energy, with billions of galaxies as islands emerging from the sea, said Fabio Governato, a University of Washington research associate professor of astronomy and a researcher with Italy's National Institute for Astrophysics.

In 1929 astronomer Edwin Hubble demonstrated that galaxies are moving away from each other, which supported the theory that the universe has been expanding since the big bang. In 1999 cosmologists reported evidence that an unusual force, called dark energy, was actually causing the expansion of the universe to accelerate.

However, the expansion is slower than it would be otherwise because of the tug of gravity among galaxies. As the battle between the attraction of gravity and the repellent force of dark energy plays out, cosmologists are left to ponder whether the expansion will continue forever or if the universe will collapse in a "big crunch."

In 1997, Governato designed a computer model to simulate evolution of the universe from the big bang until the present. His research group found the model could not duplicate the smooth expansion that had been observed among galaxies around the Milky Way, the galaxy in which Earth resides. In fact, the model produced deviations from a purely radial expansion that were three to seven times higher than astronomers had actually observed, Governato said.

"The observed motion was small, and we could not duplicate it without the presence of dark energy," he said. "When we added the dark energy, we got a perfect match."

Governato is one of three authors of a paper describing the work, scheduled for publication in the Monthly Notices of the Royal Astronomical Society, an astronomy journal in the United Kingdom. Co-authors are Andrea Maccio of the University of Zurich in Switzerland and Cathy Horellou of Chalmers University of Technology in Sweden. The work was supported by grants from the National Science Foundation and Vetenskapsrеdet, the Swedish Research Council.

The authors, part of an international research collaboration called the N-Body Shop that originated at the UW, ran simulations of universe expansion on powerful supercomputers in Italy and Alaska. Their findings provide supporting evidence for a sea of dark energy surrounding galaxies.

"We studied the properties of galaxies close to the Milky Way instead of looking billions of light years away," Governato said. "It's like traveling from Seattle to Portland, Ore., rather than from Seattle to New York, to measure the Earth's curvature."

Source: University of Washington

The ENTIRE body of findings within astrophysics and cosmology are enthralling and fascinating.

That's what I wanted to point out, the universe or more specificly the structure of the cosmos as we observe it now only makes sense if we assume the existence of Dark Energy. Thanks for posting this article And I have to agree, cosmology is one of the most interesting topic out there.